Impedance matching feeder for an antenna array



sept 8, 1959 y H. w. JAMn-:soN 2,903,695

IMPEDANCE MATCHING FEEDER FOR AN ANTENNA ARRAY Filed Jan. 20, 1954 HUGHW JM/ESON A TTORNEYS 42% mar 2,903,695 Patented Sept. 8, 1959 UnitedStates Patent-Oiice IMPEDANC'E MATCHING FEEDER FOR AN ANTENNA ARRAYApplication January 20, 1954, Serial No. 405,269

s claims. (c1. 34a-852)' This invention relates generally to antennaarrays, and more speciiically to an improved sandwich type feeder for anantenna array.

In the use of an antenna system for radiating or receiving R-F energy,maximum eiiciency of the antenna system demands that each link in thepath from transmitter to antenna, and from antenna to receiver,accurately control the R-F energy in the system in both amplitude andphase.

Prior to this time, feeders of the sandwich type for an antenna arrayhave been constructed ordinarily with junctions of simple T-shape, andhave not operated satisfactorily insofar as eicient distribution ofcurrent and power are concerned. The lumped inductance existing at thesejunctions resulted in an excessive loss of energy.

Accordingly it is an object of this invention to provide a sandwich-typefeeder for an antenna array which has a minimum of energy lossl at itsjunctions.

Still a further object of the invention isthe provision of an antennaarray feeder system wherein there is correspondence between theelectrical lengths and physical lengths of the trunk and of the feederbranches.

relation therebetween. The multibranch inner or center conductor 31 isthus contained within an enclosure formed between the bottom wall orground plane 32 of the beam forming structure 10 and an opposed wall 33.The conductor 31 is made up of a series of lines and junctions arrangedas described infra to provide feeder connections for the antenna dipolesl2--17. The couductor 3l is held in spaced apart relation from theconductors 32 and 33 as by suitable insulating spacers (not shown).Itwill be seen that the sandwich assembly is somewhat analogous to acoaxial line and comprises an outer hollow conductor 32, 33 of generallyrectangular cross-section and a flat substantially rectangular innerconductor 31.

In the feeder system 30, the conductor 31 is formed into a series ofconductive lengths. This conductor is formed into an input line 34 whichis connected through an impedance transformation, as indicated at 35, tothe trunk 37 of a Y-junction, indicated generally by the numeral 36.

-It being necessary to make a right angle turn from the line 34 to thetrunk 37, and from the trunk 37 to the branch lines 40 and 51, the trunkand the arms 38, 39 are arcuately shaped, instead of sharply angled asis the usual case. This greatly reduces the lumped inductances whichwould otherwise be present at junction 36.

1, In order to get maximum power transfer from the truuk 37 to thebranch lines 40 and 51, it is necessary that there be a minimum ofreactance at the junction point., It is an important feature of thisinvention that this is accomplished. To this end the trunk 37 and arms 38, 39 are arcuate, as described supra, to reduce the It is still afurther object of the invention to provide-a 'l feeder for an antennaarray wherein the reactance at the junctions of the feeder branches isreduced to a-minimum by cancellation thereof.

, Still a further object is to reduce the lumped inductive reactancenormally present at the junctions of a feeder for an antenna array.

Other objects and many of the attendant 'advantages of the inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l shows the general conformation of an antenna array utilizing afeeder system constructed in accordance with my invention;

Fig. 2 is a cross sectional schematic view taken along the lines II-llof Fig. 1; and

Fig. 3 is a plan view of a part of the feeder system for the antennaarray, constructed in accordance with my invention.

Referring to the drawings my improved feeder is 1llustrated as feedingan antenna having a plurality of aligned radiating-receiving elements,such as dipoles 12 17. The antenna array in the illustrated embodimenthas a reflector, generally designated 10, which may be formed ofsuitable sheet material. Dipoles 12-17 extend through openings 18 in theground plane 32. These dipoles are free at one end and suitablyconnected, as by a screw connection (not shown) at their other end tothe branches of a feeder system, generally designated 30. Externalconnection between the feeder system and a coaxial line may be made bymeans of a coaxial tting conventionally indicated at 29.

The feeder system 30 consists of a sandwich assembly made up of a pairof parallel conductive sheets 32 and 33 having a flat center conductor`31 held in spaced lumped inductive reactance at the junction, and a stub41 is provided which extends from the center of the Y- junction. Thestub 41 provides a capacitive reactance which substantially cancels theremaining lumped inductive reactance at the junction. This stub is of alength less than one-quarter wave length at the operating frequency inorder to provide a capacitive reactance, the exact length beingdependent upon the amount of inductive reactance required to becompensated.

The arm 38 connects to branch line 40 through a twostep step-downimpedance transformation, as indicated at 42, 43, the branch line 40being matched in impedance with the dipole 12.

The arm 39 connects through a two-step step-down impedancetransformation 44, 4S to the branch line 51 which'forms the trunk of asecond Y-junction, generally indicated by the numeral 50. The Y-junction50 is similar in construction to the Y-junction 36 having an arcuatetrunk 51, capacitive reactance stub 52, and arms 53, S4, which connectthrough step down transformations to a dipole feeder line 56 and thetrunk 62 of a third similar Y-junction 61. The Y-junction 61 in turnfeeds a dipole feeder line 63 and the trunk 72 of a fourth Y-junction71. The dipole feeder line 73 and the trunk 81 are connected throughimpedance transformations 74 and 75, 76, respectively, to Y-junction 71.Y-junction fed by its trunk line 81 branches off and feeds throughsuitable impedance transformations 82 and 83, 84, the dipole feederlines 85 and 86.

Dipoles 22-27 may be fed by a system (not shown) similar to system 30,and the two systems may be joined together at the input end of line 34and the corresponding line in the complementary system by a stubbed V-junction arrangement, as described in conjunction with system 30 to forma single feeder system for the dipoles 12-17 and 22-27. In such case theinput line to the trunk of this Y-junction (not shown) may be suitablymatched to the input source (not shown).

It will be apparent to those skilled in the art that more or lessdipoles would require correspondingly more or Obviously manymodifications and variations ofl the` present invention are possible inthe light of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described.

I claim:

l. A low energy loss feeder for an antenna array, said feeder comprisinga first `leg forming the trunk of a Y-junction having a pair of branchlegs, one of said branch legs being arcuate and arranged for connectionto a radiating or receiving element of an antenna array between a branchand its trunk whereby the lumped inductance at said junction is of areduced value as compared to a sharp angle junction, said junctionhaving a capacitive reactance stub extending7 therefrom to substantiallycancel the inductive reactance at said junction.

2. A low energy loss feeder for an antenna array, said feeder comprisinga first leg forming the trunk of a Y- junction having a pair of branchlegs, one of said branch legs being arranged for connection to a firstradiating or receiving element of an antenna array, the other of saidbranch legs forming the trunk of a second Y-junction having a pair ofbranch legs, one of said last mentioned' branch legs being arranged forconnection to a second radiating or receiving element of an antennaarray and the other of said last mentioned branches forming the trunk ofa third Y-junction having branch legs each of which is arranged forconnection respectively to a third and fourth radiating or receivingelement of an antenna array, each of said branches having arcuate armsat said junction to provide a smooth change in direction, each of saidjunctions having a capacitive reactance stub extending therefrom in adirection opposite to the trunk direction to substantially cancel theinductive reactance at said junctions.

3. A feeder for an antenna array, said feeder comprising la sandwich oftwo spaced apart fiat substantially parallel conductors, at least one ofsaid conductors having a Y-shaped junction having a trunk and twobranches, and a stub extending from said junction between the branchesthereof.

4. A feeder for an antenna array, said feeder comprising a sandwich ofat least two spaced apart fiat substantially parallel conductors, atleast one of said conductors having a Y-shaped junction having a trunkand two branches, and a stub extending from said junction, said stubbeing of a length less than one quarter wave length at the operatingvfrequency, whereby a capacitive reactance is set up at said junction tocancel the normally existing lumped inductive reactance thereat.

5. A feeder as defined in claim 4 wherein said branches of said junctionare arcuate in shape.

6. An antenna array feeder comprising a sandwich of two conductors, oneof said conductorsl having a, Y- junction with a trunk and two arms,said trunk being operably connected through an impedance matchingtransformer section to an input branch, andeach of said armsv feedingthrough an impedance matching transformer section to a feeder branch'matched in impedance for connectionv to a radiating element of anantenna array, and a capacitive reactance stub extending from saidY-junction, said stub having a capacitive reactance at the operatingfrequency of such value as to substantially cancel the inductivereactance at said junction.

7:. An antenna array comprising a plurality of radiatingv elements, eachof said elements being operahly connected to and fed by branches of lafeeder system, said: feeder system having any input. leg, said input legfeeding the trunk of a Y-junctionv through an impedance matchin'gtransformer, each of the arms. of said Y-junction: beingA arcuate andfeeding a branch through. anv impedance transformer, one of s-aidbranches being operably.v connected to and matched in impedance with oneof said radiating elements, the other of said branches being operablyconnected to and feeding the trunk' of a secondI Y-junction, the arms ofsaid second Y-junction feeding a trunk of a third Y-junction and asecond one of said`v radiating elements, respectively, there being aplurality of' said branch fed Y-junctions of a number equal to one lessthan the number of radiating elements, each of the arms of. one of saidY-junctions being operably con-v nected to branches matched in impedancewith and feedinga` radiating element, and a capacitive reactance stubextending from each ofV said Y-junctions between the arms` thereof tosubstantially cancelany inductive reactance at said junctions.

8. A high frequency feeder comprising an outer conductor formed bykparallel spaced conductive sheets, a multi-branch conductor insandwiched spaced apart relation between said sheets, said multi-branchconductor having Y-shaped junctions, each of said junctions having acapacitive compensating stub.

Hershberger Nov. 5, 1946 Rumsey July 8, 1952

